Pan Zoom demo widgets are layered incorrectly

[YgorSouza]

Describe the bug

Desktop (please complete the following information):

• OS: Windows 11, Fedora 39
• Browser: Firefox

[ToppDev]

maybe related. The pan zoom items can be interacted with, even outside of their window. (tested on https://egui.rs)

PanZoom.mp4

[markusdd]

closing #4448 in favor of this, thank @YgorSouza

[Creative0708]

This bug seems to be a side effect of a workaround to get the pan zoom widgets to display above the window itself.

egui/crates/egui_demo_lib/src/demo/pan_zoom.rs

Lines 113 to 132 in 2c00cb3

	let id = egui::Area::new(id.with(("subarea", i)))
	.default_pos(pos)
	// Need to cover up the pan_zoom demo window,
	// but may also cover over other windows.
	.order(egui::Order::Foreground)
	.show(ui.ctx(), |ui| {
	ui.set_clip_rect(transform.inverse() * rect);
	egui::Frame::default()
	.rounding(egui::Rounding::same(4.0))
	.inner_margin(egui::Margin::same(8.0))
	.stroke(ui.ctx().style().visuals.window_stroke)
	.fill(ui.style().visuals.panel_fill)
	.show(ui, |ui| {
	ui.style_mut().wrap_mode = Some(TextWrapMode::Extend);
	callback(ui, self)
	});
	})
	.response
	.layer_id;
	ui.ctx().set_transform_layer(id, transform);

The areas that hold the widgets are given a layer order of Order::Foreground, which displays above everything that is Order::Middle, Order::Background, etc. The demo windows are Order::Middle, so they render behind the widgets. The comments in the code snippet mention this.

If the widgets were given Order::Middle instead, moving the pan zoom window to the front (such as by clicking) would bring the widgets behind the pan zoom window:

2024-06-21.15-48-58.mp4

I'm not sure how this would be fixed without support for, say, parent/child layers. Possible feature request maybe?

[YgorSouza]

Actually, I just noticed this was already discussed in the PR that implemented the demo: #3906 (comment).